Polycyclic aromatic compounds (PAC's), which may be emitted with the effluent of combustion systems represent a potential health hazard. Some of these compounds have been shown to be toxic in laboratory tests. Dioxins, for instance, have caused severe damage to animal and plant life in laboratory experiments.
Laser induced fluorescence (LIF) is a technique which has been used in combustion research in carefully controlled laboratory-type environments for the detection of aromatic compounds in flames. In LIF, a laser photon is absorbed by a molecule and is thereby elevated to a higher electronic energy level. After some time, the excited molecule descends to a lower level. The difference in energy between the excited and non-excited states is emitted in the form of a photon.